5 ms·

Definitely not a physicist here but isn't forward time travel somewhat possible by approaching speed of light? I read about effects where if I left earth, trave

Definitely not a physicist here but isn't forward time travel somewhat possible by approaching speed of light? I read about effects where if I left earth, travelled very fast a year to me might be many to earth. Could a person not therefore 'travel fast' somewhere and come back so a place like earth had advanced significantly in time relative to them? Not sure if that is time travel in a 'jump to a new time' sense but it effectively is. And I wonder how far you could push that with theoretical technology. 1 day for 1000 years type thing...

garmaine 7y ago
We are doing forward time travel right now at a rate of 1sec/sec.
- rbanffy 7y ago
  Only from your point of view. My head and my feet travel at slightly different speeds.
  - raattgift 7y ago
    What are your head and your feet? Fluids are flowing in and out of them, outer layers are sloughing off, they're warm enough to be quite bright in infrared, potassium-40 in your head and feet are beta-decaying and so on. A decent fraction of the momentary mass in your brain may be in your feet four heartbeats later (and vice-versa). Are you implicitly considering them in some time-averaged way? (A comment similar to yours would be that your head is older than your feet because of general relativistic effects. Even if we ignore everything before you reached adulthood, there's a Ship of Theseus thing going on thanks to tissue turnover on timescales of weeks to months e.g. https://en.wikipedia.org/wiki/Bone_remodeling_period https://en.wikipedia.org/wiki/Bone_remodeling_period ).
- raattgift 7y ago
  Whose second? You and I at different points on Earth and our seconds differ. Even a decade ago we could show that a second precisely defined in the middle of the floor of a laboratory could not apply to the whole of the laboratory. "General relativity states that time speeds up for objects as gravity weakens. To demonstrate this, Chou and his colleagues raised one optical clock 33 centimetres above another. The slightly lower gravity at that height meant that compared with the reference clock, the raised clock ticked with a fractional boost in frequency of 4 × 10^–17, equivalent to a gain of 90 billionths of a second over 79 years." Even ignoring the distance between different edges of your brain and that there are humans in orbit and in mountain communities as well as below sea level, there are a number of processes in human brains that produce movement an order of magnitude faster (over short distances) not to mention people driving or flying much than the speed in this paragraph: "To demonstrate special relativity, which says that time slows down for moving objects, the researchers jolted the single atom in their optical clock so that it oscillated at relative speeds of less than 10 metres per second, or 36 kilometres per hour. This time, the clock's ticks seemed to drop by a fractional frequency of almost 6 × 10^–16." https://www.nature.com/news/2010/100923/full/news.2010.487.html https://www.nature.com/news/2010/100923/full/news.2010.487.h... (Chou et al.'s article is available at http://spiff.rit.edu/classes/phys200/lectures/dilation/chou/1630.pdf http://spiff.rit.edu/classes/phys200/lectures/dilation/chou/... and starts on the bottom of the second page of the PDF) [and cf my Finally paragraph below] Importantly when relating an ultraprecise clock on the ground with an ultraprecise clock passing above it in a blimp at, say, a constant linear ten metres per second, a Lorentz transform will need general-relativistic corrections. These corrections seem negligibly small but it seems safe to bet that in a few years they'll matter in a rack full of high end computers. Clock precision has also gotten much better http://iopscience.iop.org/article/10.1088/1742-6596/723/1/012004/pdf http://iopscience.iop.org/article/10.1088/1742-6596/723/1/01... -- "Measurements made with the rubidium fountains (and other clocks at USNO) after the first 1.5 years of continuous operation resulted in the most precise test of the universality of the gravitational redshift and enabled constraints on the coupling of fundamental constants to gravity to be improved by on average a factor of four" Meanwhile, just to plug some of the work HN's user ISL's group is doing for an extreme setup where the dependence of second not just on position on Earth but on dynamical processes in different stratified-planet layers already matters for practical purposes: https://www.npl.washington.edu/eotwash/node/17 https://www.npl.washington.edu/eotwash/node/17 ("seismic Newtonian noise ... the gravitational attraction of an optic to high density regions of the ground caused by passing seismic waves"). Finally, and also because GPS is mentioned here and there in this thread, I recommend slides 16-19 of http://web.stanford.edu/group/scpnt/pnt/PNT18/presentation_files/I08-VanBaak-GPS_Flying_Clocks_and_Relativity.pdf http://web.stanford.edu/group/scpnt/pnt/PNT18/presentation_f... If we are to insist on the notion of the flow of time, we should be aware that it poses some serious practical problems as one increases the density of marks on a chosen time axis in a dynamical spacetime like ours and populated with sources (in the Einstein Field Equation sense) like those around us. Approaching the limit of ultradense time coordinates we have to consider how parts of ourselves are sources, some organs and regions of organs being denser than others just for starters. And that's true even without getting anywhere near metaphysics and philosophical issues.

garmaine 7y ago

We are doing forward time travel right now at a rate of 1sec/sec.

rbanffy 7y ago
Only from your point of view. My head and my feet travel at slightly different speeds.
- raattgift 7y ago
  What are your head and your feet? Fluids are flowing in and out of them, outer layers are sloughing off, they're warm enough to be quite bright in infrared, potassium-40 in your head and feet are beta-decaying and so on. A decent fraction of the momentary mass in your brain may be in your feet four heartbeats later (and vice-versa). Are you implicitly considering them in some time-averaged way? (A comment similar to yours would be that your head is older than your feet because of general relativistic effects. Even if we ignore everything before you reached adulthood, there's a Ship of Theseus thing going on thanks to tissue turnover on timescales of weeks to months e.g. https://en.wikipedia.org/wiki/Bone_remodeling_period https://en.wikipedia.org/wiki/Bone_remodeling_period ).
raattgift 7y ago
Whose second? You and I at different points on Earth and our seconds differ. Even a decade ago we could show that a second precisely defined in the middle of the floor of a laboratory could not apply to the whole of the laboratory. "General relativity states that time speeds up for objects as gravity weakens. To demonstrate this, Chou and his colleagues raised one optical clock 33 centimetres above another. The slightly lower gravity at that height meant that compared with the reference clock, the raised clock ticked with a fractional boost in frequency of 4 × 10^–17, equivalent to a gain of 90 billionths of a second over 79 years." Even ignoring the distance between different edges of your brain and that there are humans in orbit and in mountain communities as well as below sea level, there are a number of processes in human brains that produce movement an order of magnitude faster (over short distances) not to mention people driving or flying much than the speed in this paragraph: "To demonstrate special relativity, which says that time slows down for moving objects, the researchers jolted the single atom in their optical clock so that it oscillated at relative speeds of less than 10 metres per second, or 36 kilometres per hour. This time, the clock's ticks seemed to drop by a fractional frequency of almost 6 × 10^–16." https://www.nature.com/news/2010/100923/full/news.2010.487.html https://www.nature.com/news/2010/100923/full/news.2010.487.h... (Chou et al.'s article is available at http://spiff.rit.edu/classes/phys200/lectures/dilation/chou/1630.pdf http://spiff.rit.edu/classes/phys200/lectures/dilation/chou/... and starts on the bottom of the second page of the PDF) [and cf my Finally paragraph below] Importantly when relating an ultraprecise clock on the ground with an ultraprecise clock passing above it in a blimp at, say, a constant linear ten metres per second, a Lorentz transform will need general-relativistic corrections. These corrections seem negligibly small but it seems safe to bet that in a few years they'll matter in a rack full of high end computers. Clock precision has also gotten much better http://iopscience.iop.org/article/10.1088/1742-6596/723/1/012004/pdf http://iopscience.iop.org/article/10.1088/1742-6596/723/1/01... -- "Measurements made with the rubidium fountains (and other clocks at USNO) after the first 1.5 years of continuous operation resulted in the most precise test of the universality of the gravitational redshift and enabled constraints on the coupling of fundamental constants to gravity to be improved by on average a factor of four" Meanwhile, just to plug some of the work HN's user ISL's group is doing for an extreme setup where the dependence of second not just on position on Earth but on dynamical processes in different stratified-planet layers already matters for practical purposes: https://www.npl.washington.edu/eotwash/node/17 https://www.npl.washington.edu/eotwash/node/17 ("seismic Newtonian noise ... the gravitational attraction of an optic to high density regions of the ground caused by passing seismic waves"). Finally, and also because GPS is mentioned here and there in this thread, I recommend slides 16-19 of http://web.stanford.edu/group/scpnt/pnt/PNT18/presentation_files/I08-VanBaak-GPS_Flying_Clocks_and_Relativity.pdf http://web.stanford.edu/group/scpnt/pnt/PNT18/presentation_f... If we are to insist on the notion of the flow of time, we should be aware that it poses some serious practical problems as one increases the density of marks on a chosen time axis in a dynamical spacetime like ours and populated with sources (in the Einstein Field Equation sense) like those around us. Approaching the limit of ultradense time coordinates we have to consider how parts of ourselves are sources, some organs and regions of organs being denser than others just for starters. And that's true even without getting anywhere near metaphysics and philosophical issues.